1. Field of the Invention
The present invention generally relates to a method for manufacturing a coordinate detector.
2. Description of the Related Art
Examples of input devices for computer systems include touch panels. The touch panel is mounted on a display, and can detect a coordinate position on the display and obtain a detection signal corresponding to the coordinate position. The touch panel allows direct, simple, and intuitive inputting.
Various systems are proposed for touch panels, such as those using resistive films, those using optical imaging, and those using capacitive coupling. Commonly used are touch panels of a resistive-film type, which are simple in structure and easy to control. There are several types of low-resistance-system touch panels depending on the arrangement of electrodes on resistive films, such as a four-wire type, a five-wire type, and an eight-wire type.
Of those, compared with four-wire or eight-wire resistive-film touch panels, five-wire touch panels are free of the problem of edge sliding, which is a defect in the four-wire type and the eight-wire type, because the conductive film of the upper substrate placed on the operation surface side is used only for reading an electric potential. Therefore, five-wire touch panels are used in an environment of hard usage or where a long useful service life is desired.
FIG. 1 is a diagram illustrating a five-wire resistive-film touch panel.
Referring to FIG. 1, a five-wire resistive-film touch panel 1 includes an upper substrate 11 and a lower substrate 12.
The lower substrate 12 includes a glass substrate 21 and a transparent resistive film 22 formed on the entire surface of the glass substrate 21. X-coordinate detection electrodes 23 and 24 for detecting coordinates of the x-axis and y-coordinate detection electrodes 25 and 26 for detecting coordinates of the y-axis are formed on the transparent resistive film 22.
The upper substrate 11 includes a film substrate 31 and a transparent resistive film 32 formed on the film substrate 31. A coordinate detection electrode 33 for detecting coordinates is formed on the transparent resistive film 32.
First, application of voltage to the x-coordinate detection electrodes 23 and 24 causes a distribution of electric potential in the directions of the x-axis of the transparent resistive film 22 on the lower substrate 12. At this point, the x-coordinate of a position where the upper substrate 11 contacts the lower substrate 12 can be detected by detecting the electric potential in the transparent resistive film 22 of the lower substrate 12.
Next, application of voltage to the y-coordinate detection electrodes 25 and 26 causes a distribution of electric potential in the directions of the y-axis of the transparent resistive film 22 on the lower substrate 12. At this point, the y-coordinate of the position where the upper substrate 11 contacts the lower substrate 12 can be detected by detecting the electric potential in the transparent resistive film 22 of the lower substrate 12.
At this point, how to distribute electric potential uniformly in the transparent resistive film 22 of the lower substrate 12 becomes an issue in this type of touch panel. Japanese Laid-Open Patent Application No. 10-83251 discloses providing peripheral electric potential distribution correction patterns in multiple stages for a uniform distribution of electric potential in the transparent resistive film 22 of the lower substrate 12.
Japanese Laid-Open Patent Application No. 2001-125724 discloses providing a common electrode so as to encircle an input surface. Japanese Laid-Open Patent Application No. 2007-25904 discloses forming an opening in an insulating film provided on a transparent resistive film and applying an electric potential through the opening.
It is desired that coordinate detectors have narrower frames because of reduction in the size of apparatuses on which coordinate detectors are to be mounted. However, it is difficult to narrow the frame of the coordinate detector described in Patent Document 1 because electric potential distribution correction patterns are provided in multiple stages in the periphery.
According to the method described in Patent Document 2, which provides a common electrode around the input surface, there is a problem in that the distribution of electric potential in the transparent resistive film is disturbed unless the ratio of the resistance of the transparent resistive film to the pattern resistance is high.
Further, according to the method described in Patent Document 3, which provides an opening in the insulating film that has been formed, the above-described problems can be solved, but the manufacturing process becomes complicated. In particular, variations in material resistances or variations in resistance during manufacture may cause a decrease in the yield of product manufacturing.